Cement additive and cement composition

Abstract

A cement additive contains industrial waste and has the effect of inhibiting formation of monosulfate in a hardened cementitious material. The cement additive contains specifically calcium carbonate, gypsum and coal ash and/or blast-furnace slag powder. This enables efficient use of industrial waste, allows inhibiting monosulfate formation in the hardened cementitious material, and allows producing a hardened cementitious material having good durability (sulfate resistance).

The invention claimed is: 
     
       1. A cement additive containing industrial waste and having an effect of inhibiting monosulfate formation in a hardened cementitious material, said cement additive comprising calcium carbonate, gypsum, and blast-furnace slag powder without coal ash,
 wherein said calcium carbonate is blended in an amount of 6 to 160 parts by weight and said gypsum (anhydrous basis) is blended in an amount of 5 to 150 parts by weight relative to 100 parts by weight of said blast-furnace slag powder, and a blending ratio (weight basis) of said gypsum and said calcium carbonate is 1:1.1 to 15. 
 
     
     
       2. The cement additive according to  claim 1 , containing blast-furnace slag powder as said industrial waste; calcium carbonate as said industrial waste and/or calcium carbonate not as said industrial waste; and gypsum as said industrial waste and/or gypsum not as said industrial waste. 
     
     
       3. The cement additive according to  claim 1 , containing limestone powder as said calcium carbonate. 
     
     
       4. A cement composition comprising the cement additive according to  claim 1 . 
     
     
       5. The cement additive according to  claim 2 , containing limestone powder as said calcium carbonate. 
     
     
       6. A cement composition comprising the cement additive according to  claim 2 . 
     
     
       7. A cement additive containing industrial waste and having an effect of inhibiting monosulfate formation in a hardened cementitious material, said cement additive comprising calcium carbonate, gypsum, blast-furnace slag powder and coal ash,
 wherein said calcium carbonate is blended in an amount of 0.5 to 160 parts by weight and said gypsum (anhydrous basis) is blended in an amount of 5 to 150 parts by weight relative to 100 parts by weight of said coal ash and said blast-furnace slag powder, and a blending ratio (weight basis) of said gypsum and said calcium carbonate is 1:0.1 to 15. 
 
     
     
       8. The cement additive according to  claim 7 , containing coal ash and/or blast-furnace slag powder as said industrial waste; calcium carbonate as said industrial waste and/or calcium carbonate not as said industrial waste; and gypsum as said industrial waste and/or gypsum not as said industrial waste. 
     
     
       9. The cement additive according to  claim 7 , containing limestone powder as said calcium carbonate. 
     
     
       10. The cement additive according to  claim 8 , containing limestone powder as said calcium carbonate. 
     
     
       11. A cement composition comprising the cement additive according to  claim 7 . 
     
     
       12. A cement composition comprising the cement additive according to  claim 8 .